Assessment of the changes in contributions from water sources to streamflow induced by urbanization in a small-sized catchment in Southeastern Brazil using the dual stable isotopes of water (18O and 2H)

Urban growth often results in changes in the urban hydrological cycle, causing impacts on water availability in densely populated regions. The water isotopologues can provide relevant information about the origin of water under different hydrogeological scenarios, aiding to implement better strategies for water conservation in coupled natural-urbanized environments. In this study, the isotopic compositions of multiple water sources were assessed in a pristine (Ipanema National Forest, FLONA) and an urbanized (Lavapes catchment, SOR) watershed located in the Sorocaba River basin (State of Sao Paulo, Southeastern Brazil), seeking to understand the causes of isotopic variability and to determine the relative contribution from different sources to streamflow, using the Bayesian mixing model approach. Differences in isotopic composition were observed, as FLONA yielded the most depleted water (ca. -7.5 parts per thousand delta O-18 for surface and groundwater and ca.+11.0 parts per thousand d-excess), while SOR yielded the most enriched water (ca.-5.5 parts per thousand delta O-18 for surface and groundwater and-3.8 parts per thousand delta O-18 for the water supply system), with evidence of evaporation (ca. + 8.2 parts per thousand d-excess). The differences observed in isotopic compositions are related to a combination of different factors, such as geological framework, groundwater recharge, and evaporation associated with the Itupararanga water reservoir. Both in FLONA and SOR, groundwater discharge is the most important factor that regulates streamflow. However, in SOR, losses from the water supply system were almost constant along the year, representing an important contribution. The results presented here highlight the use of isotope hydrology techniques to solve problems related to urban hydrology.

Automated summary

Urban growth can lead to changes in the urban hydrological cycle, affecting water availability in densely populated regions. The use of water isotopologues can provide valuable information about water sources and aid in implementing better water conservation strategies in urban environments. This study assessed the isotopic compositions of water sources in both a pristine and urbanized watershed, highlighting the importance of isotope hydrology techniques in understanding and managing urban hydrology.